The present invention concerns an apparatus and a method for mechanically joining metal sheets, profiles and/or multi-sheet joints lying on top of each other, wherein joining tools are moved by power means toward the parts to be joined and a joint is made between the parts to be joined by the force effect of the joining tools.
Mechanical joining techniques for connecting parts to be joined such as for example metal sheets are increasingly gaining in importance, as they have some advantages specific to the method. Patent DE 197 01 252.3 describes a method as well as connecting means for joining metal sheets by punch riveting. For this it is explained inter alia that punch riveting of 1 mm. sheets of ZSTE 420 material requires forces of 74 kN which are not attainable with ordinary riveting machines. The solution proposed there, of providing the rivet with a blunt circular or annular front surface with which the metal sheets are pierced, allows a reduction of the necessary work forces compared with the state of the art known at the time. Also the lateral or angular offset of the tools or tool portions, which would reduce the joint quality or make a connection completely impossible, is reduced by the shot-like operation. Whereas this process perfectly reduces the lateral or angular offset, the drawback of the shot-like operation lies in that considerable measures must be taken to make it safe to use. The propellant charges which are used for the shot-like operation are potentially, in case of improper handling, not completely risk-free.
In patent DE 197 18 576 are described an apparatus and a method for mechanical joining techniques. In particular in FIGS. 4 and 5 is shown a typical force/displacement graph for the working movement of the stamp. Patent DE 197 18 576 however instructs only that individual or several working members for making a mechanical joint can be controlled or regulated in their movement and/or force, but without going into the basic problem of reducing the high forces for making a mechanical joint. According to the state of the art described there, the transforming energy required is applied by hydraulic cylinders which make the respective joint in a single quasi-continuous stroke movement. This publication contains no indication as to how the method and the apparatus for making joints can be improved by weaker joining forces.
Accordingly it is an object of the present invention to provide an apparatus and a method for mechanical joining which allow weaker reaction forces in the making of the mechanical joint.
It is a further object to provide an apparatus and a method for mechanical joining which allow a correspondingly lighter design and easier handling of the joining tools.